I am not a "VW" guy, but I have rebuilt a muultitude of engines. There are ways to build small bits of hp beyond an normal IT engine all it takes is money and time.
Intake length, collector lenght, primary length, valve seat, valve springs, final hone finish, piston rings, pistons, head gasket, bearings, oil, windage, passive evac, blue printing, the list goes on and on. All can make power and or result into a more balanced/smoother engine when used correctly together. It is all the same things that companies like sunbelt, Robelo, RE, Roher morrison, etc.. all do.